Colorimetric gas sampler-analyzer



Jan. 17, 1961 F. R. SMITH 2,968,536 Y COLORIMETRIC GAS SAMPLER-ANALYZERFiled Feb. 6, 1957 2 Sheets-Sheet 1 'Ill lill

Jan. 17, 1961 F. R. sMn-H 2,968,536

coLoRIMETRIc GAs SAMPLER-ANALYZER Filed Feb. 6, 1957 2 SheetsSheet 2 w3o LEU Ouf z R R I 2o AIR sAMr ER-\NA| ZER,cs2 g sET FLow METER To 6.2 oRUN 5 MINUTES E .o

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COLORIMETRIC GAS SAMPLER-ANALYZER Frederick R. Smith, Nitro, W. Va.,assigner to American Viscose Corporation, Philadelphia, Pa., acorporation of Delaware Filed Feb. 6, 1957, Ser. No. 638,619

4 Claims. (Cl. 23-254) This invention is directed to a novel gassampleranalyzer. More particularly it is directed to a process andapparatus for rapidly and accurately determining the CS2 concentrationin the atmosphere.

In rayon and cellophane mills which employ large quantities of CS2 toform cellulose Xanthates it is necessary to periodically measure theconcentration of CS2 in the atmosphere to prevent its reaching a levelwhich is toxic to the workmen.

The usual system for analytical control of CS2 concentrations in rayonmills requires the services of an air sample boy and an analyst. Thesamples are taken in sets of six to eight, this being about the limitingnumber one air sample boy can handle. Approximately one half hour isrequired to prepare absorbing solutions and towers and assemble theminto the sample boxes. Each sample taken for CS2 measurement requires100 ml. of copper diethylamine reagent. Thus, preparation to takesamples requires 600-1600 cc. of reagents, and about one half hourstime. The sample boxes are then transported to the various samplinglocations, a second trip made to assemble tubing and air pumps asnecessary, and the samples set up and started. This requires from l to30 minutes. The sampling is continued for one hour during which time theboxes are rechecked occasionally to maintain their proper functioning.At the end of the hour, the sampling is stopped, the rubber tubing andair pumps returned to their appointed places and the samples transportedto the laboratory. They are there disassembled and processed through thenecessary analyses. The results are then available two to three hoursfrom the time they are started. Add this to the time needed for solutionpreparation, cleaning equipment, and replacement of glassware, and it isevident that a considerable effort is expended in the analytical controlof gas concentrations. Using this system, special and check samplesoften have to be scheduled for half to a day later than the originalsample. In the meanwhile, it is very likely that the situation willchance, and the source of the high concentration never be known. Use ofthe sampler-analyzer described in this application would eliminate mostof these scheduling diihculties.

Accordingly it is an object of the present invention to provide a methodand means for rapidly and accurately determining the concentration ofany desired gas in a mixture of gases. A further object is the provisionof a gas sampler-analyzer which is adapted for grab-sampling and issimple, compact and portable. A more specific object is the provision ofmeans for collecting small samples of CS2 and analyzing themquantitatively in a matter of minutes.

The invention is best illustrated by reference to the drawings whereinFigure l is a back view showing an assembly embodying the invention in'`as simplified a form as possible.

Figure 2 is a calibration curve which plots the meter reading inmicro-amperes against p.p.m. (parts per million) CS2 over a fixed andspecified time and flow rate; l

In general, the invention may be described as follows: A sample of gasfrom any source containing CS2 is pumped at a constant rate through anH2S-scrubber and then into the base of a small bore vertical absorber ordiffusion tube lled with an absorber reagent, that is, one which reactswith CS2 to develop a color which may be measured by means ofphotoelectric cells. As stated above the reagent for CS2 may be copperdiethylamine. Por simplicity the invention will be described withrespect to CS2 analysis, it being understood that the same basic processmay apply to the analysis of other gases. The inner diameter 'of theaforesaid Vertical diffusion tube is small enough so that the gas whichis pumped into its base below the liquid level therein is confined intobubbles of the diameter of the tube. As these bubbles rise in the tubethey force some liquid to rise ahead of them. Using a short enough tube,the liquid may be pumped from the tube by this action. The dischargedliquid is then caught in a funnel, the base of which drains into theabsorber tube at a point below that where the sample gas is introducedthereto, so that the liquid is continuously recycled to the absorber.The gas bubbles, however, escape from the top of the funnel and arepumped out of the system. Adjacent the funnel is positioned a column offresh absorber liquid, i.e., liquid which has not been reacted withCS2-containing gas. Separate beams of light from the same source arepassed through both reagent columns and the respective beams then passedonto separate photoelectric cells. The difference in intensity of thelight reaching the two photoelectric cells is measured by an electricalsystem which records the difference upon a potentiometer or similardevice.

Referring to Figure l, the analytical elements are housed in a box l0having sidewalls lll, a floor l2, and a handle i3. Pump 37 draws samplegas through the system and is powered by a motor 3S. Pump 37 may be anytype of gas pump such as a diaphragm pump. In one embodiment of thesystem this pump has a ce.- pacity of 225 cu. in./min. The aircontaining CS2 is drawn by pump 37 through line Ztl, through owmeter 21,and into the base of H2S-scrubber Z3.

Flowmeter 2l is not illustrated in detail but preferably the owmeter isa glass tube having a tapered bore and calibrations marked along itslength. A sapphire ball is placed in the tube and the tube positionedvertically with the narrow end at the bottom.. When air passes into thenarrow end, its How upward will cause the ball to float at a point alongthe tube which is related to the volume of air flowing. Line 2d opensinto the base of scrubber chamber 23 through a suitable diffusion meanssuch as a sintered glass filter 22. Scrubber 23 is iilled with anysuitable liquid for removing H25 from the gas stream, of which thepreferred ones are cadmium acetate and CdCl2, These reagents remove anyH23 which would react with diethylamine solution to give a color and acorrespondingly higher result for CS2 concentration. Column 23 can beopened for draining and refilling whenever necessary by opening valve24.

Desulded air is pulled from the top of column 23 through line 25 intodiffusion chamber 27. This may take the form of a Vigereaux distillationcolumn having vertical rows of iins 29 projecting from the inner wall ofthe coltunn so as to describe a tortuous zig-zag opening through thevessel. A delivery tube 3@ connects the top of vessel 27 with a funnel3l and is sealed into the side of funnel 31. Tube 30 carries the streamof gas bubbles, alternating with globules of reagent solution, fromcolumn 27 into the top of funnel 31 wherein the gas bubbles, nowstripped of their CS2 content, separate from the liquid and are drawnoii through line 32 to pump 37 where it is vented to the atmospherethrough "line 39. Line 32 contains a T-tting l0 in combination with acontrol valve 41 which can be adjusted to regulate the iiow rate throughthe system. Delivery tube 30 is bent to the horizontal where it entersfunnel 31 to effect more efiicient separation of gas bubbles from theliquid. The liquid reagent drains down through the stern 43 and throughoptical absorption cell 44 and is recycled to diffusion chamber 27 viareturn pipe 46. Funnel 31 must be small enough that it does not addexcessively to the volume of the unit but deep enough to achieveseparation of the gas and liquid delivered to it. While operating theremust always be a pool of liquid in the funnel so that no air is carriedto absorption cell 44, since this would interfere with the measurement.

The reagent supply 50 is contained in a reagent reservoir 51, which ispreferably of polyethylene or other light-weight plastic material.Reservoir 51 is stoppered at 52 and designed to discharge through line53 to a second absorption cell 54 which serves as the reference cell forthe analyzer or colorimeter. Cell 54, in turn, discharges the reagentliquid through line 56 to the intake side of two-way stopcock 57. Theoutlet orifice of stopcock 57 connects to drain pipe 58, whichdischarges used reagent from lines 46 and 47 to receptacle 59,preferably of polyethylene or other plastic composition. Receptacle 59is fitted with a breather tube 601. A new reagent solution is drawn fromreservoir 51 into line 53 each time the absorbing unit is recharged,which is effected by turning the handle of stopcock 57 so as to closeoff drain pipe 58 and provide an open connection between line 56 andline 47. When the stopcock handle is turned to the other position, itwill close off line S6 and permit line 47 to drain through line 58. Atan intermediate position it disconnects all three lines 56, 47, 58 fromeach other and permits reagent from line 46 to bypass line 47 and enterthe base of absorber 27.

The analyzer means is indicated schematically; being of ratherconventional design this feature is not claimed to be patentable per se.Basically the analyzer as referred to from here on and in the claimsconsists of the two absorption cells 44, 54 and a light source 65 whichincludes two sets of condensing lenses 66, 66a, one for each photocell67, 67a of the analyzer. A slot is provided between the absorption cellsand photoelectric cells for insertion of a filter and an optical stop(not shown). This is schematic, of course, the filter and shutter unitsactually being built-in. Leads 68, 68a connect in known manner to anammeter 70. Knob 71 controls a pair of variable resistors in the lightcircuit, hence can be set so as to adjust the light output and thus thefull scale position of the ammeter 70. A main switch 72 activates thecircuit,

Photocells 67, 67a in a preferred embodiment are a matched pair of Aselenium self-generating photocells sold by International RectifierCorp. Ammeter 70 may be an 0-50 micro-ampere panel type meter. The lightsource 65 need be no more than a 5 cell iiashlight bulb supplied withcurrent from the secondary of a door bell transformer. Lenses 66, 66aare double convex and a typical dimension would be 26 mm. diameter and28 mm. focal length.

PREPARATION OF SOLUTION FOR CALIBRATION gms. OS2 mol. wt. CS2 24.45 isthe molecular volume, assuming an average Liters of CS2 vapor= 24.45

Liters of OS2 Liters of sample If time and sampling are constant, thenAmmeter reading 1 Concentration l Ammeter reading 2 Concentration 2 Toprepare a calibration chart, a series of solutions of known CS2 contentare placed in the unit. In each case the absorbing unit is charged withfresh reagent by adjusting two-way stopcock 57 so as to connect line 47with line 56. The light 65 is turned on, the sample pump 37 is turnedon, the sample flow adjusted and the time recorded. At the end of thedesignated time, the sampling is stopped, reading recorded, and the usedreagent drained into lines 47, 58 to receptacle 59. The absorbing unitis rinsed and the sampler-analyzer is ready for the next sample. Asshown in Figure 2 the time may be set at 5 minutes and the reading offlowmeter 21 set at 6, `which might correspond to 500 cc./min. Figure2is a graph obtained from a series of samples of known CS2concentration.- Other curves of this type could be obtained by changingthe variable, as by holding the ammeter reading constant and varying thetime of sampling.

For routine control use the instrument is conveniently operated for aset period of time at a constant iiow rate, so that the ammeter readingcan be readily translated into p.p.m. CS2 (Fig. 2). It will be readilyobserved which samples are higher than the desired limit condition andfurther tests can be made without delay. This will achieve bettercontrol of the gas concentrations in an area than is now possible. Whena sample is obtained which gives an excessively high reading, using theiixed time method, the samples can be proved by use of a variabletime-fixed meter reading calibration.

The invention can be further illustrated by the following example.

Example Fill the reagent reservoir 51 with a freshly prepared solutionof copper diethylamine in methyl Cellosolve. Ten cc. of this solutionwill absorb and react with l litre air sample containing 120 ppm. ofCS2. Fill the H28 scrubber 23 half full of 10% cadmium acetate solution.Turn stopcock 57 so as to iill absorber column 27 with reagent, thenturn stopcock 57 off. The absorbing unit 27 should be filled so that atthe desired flow rate of air, the circulation will be maximum and noentrainment of gas bubbles in absorber liquid is noticed. Turn on pumpmotor 38. Turn the iiow control valve 41 until the desired flow isindicated by the fiow meter 21. Close the optical stop or shuttercontrol and turn on and adjust analyzer light 65 so as to adjust meter70 to full scale. Remove the optical stop by opening the shuttercontrol. Time the sample and read the meter at the end of the samplingperiod. Enter meter reading on calibration chart (Fig. 2) to determinep.p.m. of CS2. Turn sample flow control valve 57 to drain used reagentto waste tank 59, and instrument is ready for refilling and reuse.

The apparatus described should be considered as illustrative of theinvention, not limiting, since various modi fications could be made bythose skilled in the art Without departing from the basic concept of theinvention. Thus, one might analyze for gases other than CS2 by employingthe appropriate reagent.` In place of using the acetate or chloride ofcadmium to precipitate the H2S one could use other salts such as thesulfate, nitrate, formate, oxalate, halide, etc. Instead of usingcadmium as the cation one could use many other metals such as Pb, Hg,Fe, Zn, Cu, Mn, Co, Ni, etc.

I claim:

1. A portable testing device comprising a case, a carrying handle onsaid case, apparatus mounted within said case for facilitating thebatch-wise analysis of the amount of a gaseous impurity in the air, saidapparatus comprising a reservoir containing a supply of an indicatorliquid which changes color in the presence of the gaseous impurity, saidreservoir being mounted in the upper portion of said case so that theliquid may flow therefrom by gravity, a vertical reaction chamber, aiirst liquid transmission line extending parallel to said reactionchamber, said transmission line having an enlarged upper chamber, asmall bore tube connecting the upper end of said reaction chamber to theenlarged upper chamber of said transmission line, a lower lineinterconnecting the lower end of said transmission line and the lowerend of said reaction chamber, a second liquid transmission lineextending from said reservoir to said lower line, valve means betweensaid second liquid transmission line and said lower line, said valvemeans being operable to connect said second liquid transmission line tosaid lower line and to disconnect it therefrom whereby said reactionchamber and said first liquid transmission line may be lled with freshindicator liquid and then disconnected from the reservoir supply, aconduit opening into the lower end of said reaction chamber for feedingthe air to be tested for the gaseous impurity into said reaction chamberwherein the gaseous impurity is reacted with the indicator liquid as theair passes upward through said chamber, said indicator liquid beingmoved upward in said small bore tube by the air and discharged into theenlarged upper chamber of said first liquid transmission line, means forwithdrawing the air from said enlarged upper chamber whereby continuedintroduction of air into the lower end of said reaction chamber causesthe indicator liquid to circulate through the reaction chamber and thefirst liquid transmission line and gradually change color as it isreacted with more and more of the gaseous impurity, and a photoelectriccomparison system mounted in said case, said system including an opticalabsorption cell in each of said transmission lines and means forcomparing the color intensities of the liquid in said cells.

2. The device of claim 1 wherein a receptacle is mounted in the lowerportion of said case and there is means for discharging the reactedindicator liquid from the reaction chamber and the rst transmission lineinto said receptacle after a test is completed.

3. The device of claim 2 wherein the means for discharging the reactedindicator liquid includes said valve means which is a three-way valveoperable to connect said lower line with said receptacle.

4. The device of claim l wherein the means for withdrawing air from theenlarged upper chamber of said rst liquid transmission line comprises atube connected to said chamber, a pump for pumping the air through saidtube, and a control valve in said tube for regulating the rate of flow.

References Cited in the le of this patent UNITED STATES PATENTS2,328,461 Kienle et al Aug. 31, 1943 2,382,381 Calvert et al Aug. 14,1945 2,395,489 Major et al. Feb. 26, 1946 2,413,261 Stackhouse Dec. 24,1946 2,430,895 Tuve et al. Nov. 18, 1947 FOREIGN PATENTS 802,586 FranceJune 13, 1931 OTHER REFERENCES Brady: Anal Chem. 20, 1033-37 (1948).Karasek et al.: Anal. Chem., vol. 28, N0. 2, pp. 233-236, February 1956.

Morehead: Ind. and Eng. Chem, Anal. Ed., vol. 12, No. 6, 1940, Pp-373-374.

1. A PORTABLE TESTING DEVICE COMPRISING A CASE, A CARRYING HANDLE ONSAID CASE, APPARATUS MOUNTED WITHIN SAID CASE FOR FACILITATING THEBATCH-WISE ANALYSIS OF THE AMOUNT OF A GASEOUS IMPURITY IN THE AIR, SAIDAPPARATUS COMPRISING A RESERVOIR CONTAINING A SUPPLY OF AN INDICATORLIQUID WHICH CHANGES COLOR IN THE PRESENCE OF THE GASEOUS IMPURITY, SAIDRESERVOIR BEING MOUNTED IN THE UPPER PORTION OF SAID CASE SO THAT THELIQUID MAY FLOW THEREFROM BY GRAVITY, A VERTICAL REACTION CHAMBER, AFIRST LIQUID TRANSMISSION LINE EXTENDING PARALLEL TO SAID REACTIONCHAMBER, SAID TRANSMISSION LINE HAVING AN ENLARGED UPPER CHAMBER, ASMALL BORE TUBE CONNECTING THE UPPER END OF SAID REACTION CHAMBER TO THEENLARGED UPPER CHAMBER OF SAID TRANSMISSION LINE, A LOWER LINEINTERCONNECTING THE LOWER END OF SAID TRANSMISSION LINE AND THE LOWEREND OF SAID REACTION CHAMBER, A SECOND LIQUID TRANSMISSION LINEEXTENDING FROM SAID RESERVOIR TO SAID LOWER LINE, VALVE MEANS BETWEENSAID SECOND LIQUID TRANSMISSION LINE AND SAID LOWER LINE, SAID VALVEMEANS BEING OPERABLE TO CONNECT SAID SECOND LIQUID TRANSMISSION LINE TOSAID LOWER LINE AND TO DISCONNECT IT THEREFROM WHEREBY SAID REACTIONCHAMBER AND SAID FIRST LIQUID TRANSMISSION LINE MAY BE FILLED WITH FRESHINDICATOR LIQUID AND THEN DISCONNECTED FROM THE RESERVOIR SUPPLY, ACONDUIT OPENING INTO THE LOWER END OF SAID REACTION CHAMBER FOR FEEDINGTHE AIR TO BE TESTED FOR THE GASEOUS IMPURITY INTO SAID REACTION CHAMBERWHEREIN THE GASEOUS IMPURITY IS REACTED WITH THE INDICATOR LIQUID AS THEAIR PASSES UPWARD THROUGH SAID CHAMBER, SAID INDICATOR LIQUID BEINGMOVED UPWARD IN